IPOD Stereo Connection COAX

December 12, 2006 9:14 AM

IPOD connection to stereo through RCA - COAX - RCA plugs. Does anyone have experience connecting an IPOD directly to the stereo over a 30 - 40 ft distance using COAX and the resulting sound quality?
posted by strangej to Technology (8 answers total)

I don't have direct experience with this, but I do home recording and I have experience with long cable runs.

Coax might sound OK over that distance because the cables are designed to reject noise. However, over long runs, I usually use balanced connections over regular 3-conductor cable. A balanced connection takes the input signal, inverts it, and transmits both the regular and the inverted signal. Since noise will be added to both the regular and the inverted signal, it cancels out when you re-invert the inverted signal and add them together. Basically you start with A, and transmit both A and -A. The signals become, respectively, A+N and -A+N. Invert the second signal and add, and you get (A+N) - (-A+N) = A + N + A - N = 2A which is fine. You can make exceptionally long runs this way with little noise.

The output from your ipod, and the inputs to your stereo, are unbalanced connections. However, you can output from the ipod into a unbalanced-to-balanced converter, and have a balanced-to-unbalanced converter at the connection point to your stereo.

This might all be overkill. 40 feet of coax cable costs something like $10-20 so maybe just try it?
posted by RustyBrooks at 10:23 AM on December 12, 2006

I connect an ipod and laptop to the stereo over a 1/8" headphone ->RCA -> coupler -> 50ft RCA cable arrangement. It sounds just fine, and the cable was cheap from cablesforless.com. (no affiliation, just a happy customer.)
posted by wzcx at 10:41 AM on December 12, 2006

"Coax" is a very vague term. Do you mean RG-6? RG-59? I guess it's possible, but those are both designed to carry RF signals, not baseband, so it's kind of putting the square peg in the round hole. And how are you going to modulate the stereo signal over the single conductor? For a small distance of 40 feet you should be able to just get a spool of shielded stereo wire for about $10 at any radio shack that would work much better, as it doesn't need to be modulated in any way.
posted by Rhomboid at 10:42 AM on December 12, 2006

Response by poster: Sorry, the coax would be RG-6. I am probably wrong but I thought I could use 4 RCA Female to "F" Female gold plated connector's in the walls to the plates. Then I would use a stereo to RCA connector from the IPOD and RCA cables for the hole house audio reciever. I will probably take a look at the 50ft RCA cable from cablesforless.com.

[IPOD stereo-RCA cable] - [RCA-F connector - F-RCA connector] - [RCA cables to stereo]

Thanks all.
posted by strangej at 10:53 AM on December 12, 2006

But unless you're talking about using two RG-6 cables you still haven't addressed how you plan to multiplex both left and right channels on a single conductor.
posted by Rhomboid at 11:04 AM on December 12, 2006

I have my computer (occasionally my iPod) connected to my stereo using fairly long run of unbalanced cable. The biggest problem that I ran into was 60Hz hum, but I mostly solved it by playing around with how I grounded everything.

If you have fluorescent lights or a computer in the same room, that's going to exacerbate the situation. A 1/8" extension cable (20' or so each) is quite cheap from RadioShack, so I don't think there's any reason not to just give it a try. If they hum like crazy, just return them and you can give a balanced configuration a try.

Using shielded, balanced lines (with two matching transformers on each end, one each for L and R) is without a doubt the "right" way to do things...but you can always give the cheap way a shot first and see if it works for you.

Alternately, there is a 'middle of the road' approach, where you could use an unbalanced signal but use a shielded cable (where the signal ground is a separate wire from the shield). That sometimes cuts down on hum, and might be sufficient for your application provided your house isn't really electrically noisy.

I guess if I were you, I'd start off with the inexpensive methods and work up until the problem goes away and the quality is acceptable to you. However if you don't enjoy tinkering and you just want to save time, you'd want to get two 2-channel audio baluns (like the Jensen PC-2XR, sticker shock warning), and two 40' runs of XLR cable.

Preview: RG-6 or RG-8 coax is not really what you want for this. Those types of coax only have a single central conductor, so you'll need to run two of them, and unless you're buying really good stuff, the shielding isn't even that good. You'd be better off getting something like Belden 8412 (if that link doesn't work, just Google it), one line per channel. That will give you good shielding, plus the ability to run balanced signals if you need to.
posted by Kadin2048 at 11:17 AM on December 12, 2006

Response by poster: Yes I was talking about using two RG-6 cables. I will try the cheap radio shack version and see how it sounds.
posted by strangej at 11:40 AM on December 12, 2006

Whoa, 30 to 40 feet runs of coax are going to have a fairly high capacitance which will likely result in high frequency rolloff. I wouldn't do it. I would go with something like a shielded twisted pair, 18 gauge solid core preferred. Ground the shield at the source only.
posted by caddis at 11:54 AM on December 12, 2006